I joined this forum to allow some relevant info to flow freely out to fellow jeepers, so here it comes:
I have a 1989 Cherokee 4.0L that "suffered from" poor to non existent heater temps and a very erratic temp guage for the first two and a half years I've owed it. Bought in Nov 2008.
Upon reading page after page of forum postings about Cherokee owners experiencing poor heat and/or erratic temp guage readings and non corrective responses from mechanics and do it yourselfer's I decided to figure the problem out so please read the following:
I worked at Chrysler Jeep Engineering for almost 19 years, up until the 2008 fiasco.
This is simply a problem of internal bureaucracy with the attitude of "if it works or sorta works, let's not go further than that.....especially if there is cost associated to do so."
So, even after I installed a new heater core the problems continued.
The following should correct the issues of no heat and/or irradic temp guage readings:
Look at my posted photo and simply compare it to your vehicle. THE HEATER CORE PLUMBING AND OVERFLOW TO HEATER HOSE "STEEL Y TUBE IS REVERSED" on every vehicle produced. The steel "Y" tube must be relocated and afixed as in the picture. This will require some creativety on your part with hose splice connectors.
In short, the intake side of the heater core is now on top instead of below. (THINK) ....It is difficult for water to flow upwards in the internals of the heater core even under flow pressure, given there is an alternate open straight path into the overflow bottle.....
NOTE: If after time the guage reading does drop off upon driving and then goes up towards 210 then you need to add coolant to the bottle. The system probably burped up some residual trapped air.
Remember, this system is non pressurized and trapped air can take some time to move it's way out.
End result: Great heat in the winter months and no more erratic temp guage readings. Try the fix and be warm this winter.

 

Very interesting.

I have a 98 with the same issues but aren't they different cooling/heating systems, an open system as opposed to a closed?

I do not have the steel Y like in your picture.

The tube comes directly out of the engine into the heater core and directly back to the engine.

Please advise, it's starting to get cold!

 

How is the orientation of hoses connected to the heater core ??

There is a good chance the heater core might be hooked up backwards with the inlet (flow in) on the bottom of the core.

Take a look.

 

The top hose coming out of the thermostat housing goes to the top port in the fire wall(assuming the in of the heater core)

If reverse the hoses going into the heater core what will happen?

 

i meant to say "if I take the hoses and reverse the hose going into the heater core, what will happen?"

 

Let me do some looking around for the 98 orientation. I'll post after I get back from class tonight.

 

x2 on my 97. Heat works but not well. Interested to find out if this is a easy fix.

 

On a '98 (probably other years as well), there are two different size heater core nipples at the firewall and different size heater hoses as well.....5/8" and 3/4". Kinda hard to get 'em backwards but I guess anything's possible. '97 up don't have a vacuum operated heater control valve at the firewall.